This application is based upon and claims the benefit of Japanese Patent Applications No. 2000-45135 filed on Feb. 17, 2000, and No. 2000-181665 filed on Jun. 16, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a fuel cell system including a fuel cell that generates electric energy by a chemical reaction between hydrogen and oxygen, which is effectively applicable to a movable body such as vehicles, ships, and portable generators.
2. Description of the Related Art
A fuel cell generates an electric power by a chemical reaction between hydrogen and oxygen that are supplied in accordance with a required electric power. However, it is difficult to utilize hydrogen supplied to the fuel cell at 100%, and non-reacted hydrogen is discharged together with exhaust gas (water vapor, carbon dioxide, and the like). Generally, an amount of hydrogen supplied to the fuel cell is set at a value larger than a theoretical value in consideration of the amount of non-reacted hydrogen. Because of this, it is difficult to decrease the amount of non-reacted hydrogen discharged from the fuel cell.
The present invention has been made in view of the above problem. An object of the present invention is to decrease an amount of non-reacted hydrogen that is discharged from a fuel cell.
According to the present invention, briefly, hydrogen is supplied to a fuel cell intermittently in accordance with an amount of hydrogen consumed in the fuel cell.
Preferably, a discharge passage valve (second valve) is provided in a hydrogen discharge passage through which hydrogen containing gas is discharged from the fuel cell as exhaust gas. The discharge passage valve opens or closes the hydrogen discharge passage based on the amount of hydrogen consumed in the fuel cell.
More preferably, an inflow passage valve (first valve) is provided in a hydrogen inflow passage, and opens or closes the hydrogen inflow passage. The hydrogen inflow valve is opened to supply hydrogen to the fuel cell when the hydrogen concentration in the fuel cell is equal to or less than a first concentration. The discharge passage valve is closed to stop supplying the hydrogen to the fuel cell when the hydrogen concentration detected in the fuel cell is equal to or larger than a second concentration larger than the first concentration.
Accordingly, when the hydrogen concentration in the fuel cell is high, hydrogen stays in the fuel cell to be sufficiently reacted, and when the hydrogen concentration in the fuel cell is low, hydrogen is further supplied to the fuel cell. Consequently, an amount of non-reacted hydrogen discharged from the fuel cell can be reduced.